Electronic circuits, particularly digital logic circuits used in computers, have been extensively miniaturized, and continue to be miniaturized. In digital computer logic circuits, multi-layer wiring systems are frequently employed. The multi-layer wiring systems include integrated circuits containing active components which perform required logic functions. The integrated circuits are mounted on the surface of a ceramic plate, generically termed a substrate, carrying conductors that establish different interconnections between access terminals of different integrated circuits. The substrate, in addition to carrying integrated circuits, frequently carries other components, particular capacitors, having dimensions larger or smaller than those of the integrated circuits. The conductors are generally referred to as printed circuit conductors and are deposited on the substrate by a serigraphy, i.e., silk screen, process. Occasionally, a substrate must undergo wiring modifications, either during or after production.
The substrate structure is so devised that any wiring modification may be made by acting only on external connection layers of the substrate, as the external layer is the only layer which is readily available. Thus, it is not possible to modify the internal substrate layer of a multi-layer wiring system. To enable the wiring to be modified, all components mounted on the substrate have access terminals connected only to the external layer. Thus, it is possible to modify the wiring of the multi-layer wiring by isolating particular parts of a previously existing interconnection circuit of the multi-layer wiring. To sever a conductor from the external interconnection layer of the substrate in such a manner that one of the access terminals of an integrated circuit is completely isolated without deteriorating the remainder of the wiring system and/or active components implanted on the substrate, the apparatus disclosed in the copending, commonly assigned application of Maurice Devoille, entitled "Method of And Apparatus For Severing Printed Circuit Conductors" was devised. The present invention is directed to an apparatus for and method of placing complementary circuit elements on the surface of a substrate, to modify the wiring system carried by the substrate.
With existing machines, it is possible to solder a stripped end of an insulated wire to a surface of a conventional printed circuit board. With the prior art machines, the wire is applied to the board in a path between two terminals which are to be electrically connected and are firmly attached to the board. The electro-mechanical machines of the prior art have been found unsuitable and too imprecise to be adaptable, without fundamental alteration, to produce an analogous wiring system on a multi-layer substrate of a few square centimeters. One of the problems with the prior art devices is that they are incapable of handling wire of the order of a few hundredths of a millimeter in diameter, as employed in complementary multi-layer wiring systems. The machine in accordance with the present invention has been developed to handle such wiring chores.
It is, accordingly, an object of the present invention to provide a new and improved apparatus for modifying and/or completing printed circuit wiring applied to printed circuit boards which carry substrates for integrated circuits and other micro-miniaturized components.